Microwave switching circuit



Aug. 19, 198

.3. T. FRASER MICROWAVE SWITCHING CIRCUIT Filed April 9, 1955 INVENTOR.

JUL/U5 TF/Q/i-Sf/Q United States Patent Ofihce 2,848,688 Patented Aug.19, 1958 MICROWAVE SWITCHING CIRCUIT Julius T. Fraser, Ossining, N. Y.,assignor to General Precision Laboratory Incorporated, a corporation ofNew York Application April 9, 1956, Serial No. 577,022

5 Claims. (Cl. 333-7) This invention relates to apparatus for switchingmicrowave energy from one to another transmission path.

In the past there have been known microwave switching devices whichdepend for their action upon the ionization of gases under low pressure.Such switches are usually arranged to be actuated by the presence of apredetermined power level within the waveguide and, although this kindof actuation is suitable for some purposes, it is frequently desirableto switch the wave energy regardless of the amount of power beingtransmitted. To meet this need, switches involving the movement ofmechanical elements have been devised but these are inherently slow inoperation, the speed being limited by the Another object is to provide amicrowave switch which is compact.

In accordance with the invention, two short slot" hybrid junctions areaxially aligned. In to the coupling space in one of the hybrid junctionsis placed an element which is active in the Faraday magneto opticalsense. A magnetic field is applied to this element and variation in itsstrength and direction causes a corresponding variation in the divisionof power between the two output arms.

For a clearer understanding of the invention reference may be made tothe following detailed description and the accompanying drawing inwhich: 7

Figure l is an isometric View of a preferred embodiment of theinvention; and

Figure 2 is a horizontal cross sectional view taken on the plane 22 ofFigure 1.

Referring now to the drawing, there is shown a structure comprisingbasically two standard rectangular waveguides arranged side by side andhaving a common narrow wall or side 11. A portion of the common wall iscut away to form a coupling space 12 within the structure, beyond whichthe wall reappears as shown at.13. Thus there are defined four waveguidearms A, B, C and D. In the region of the coupling space 12 the outernarrow walls 14 and 15 are drawn slightly toward each other as shownsomewhat exaggerated at 16 and 17. Each broad side 18 and 19 has a smallprotuberance, one of which is shown at 21, in the center of the couplingspace to aid in matching the discontinuity.

The apparatus so far described has come to be called in the absence ofthe coupling space 12, while the energy in arm D will be advanced inphase by 135 with respect to its original phase. The junction issymmetrical and a similar division of energy would take place ifmicrowave energy were introduced into any other arm. This hybridjunction per se has been described in the literature and is not thesubject of the present invention. For further details reference may bemade to an article by Henry J. Riblet entitled The Short Slot HybridJunction, published in the Proceedings of the I. R. E., volume 40, No.2, February 1952, page 180, and to an article by Harold Heins entitledRadar Duplexer Uses Dual TR Tubes, published in Electronics for August1954, page 149.

Referring again to the drawing, the common wall 13 is continued alongthe axis of the structure for a short distance and then is again cutaway so as to form another coupling space 23 which space, together withthe remaining walls, defines a second short slot hybrid junction havingarms, C, D, E and F. As before, the outer narrow walls are drawntogether slightly and two protuberances, one of which is shown at 24,are provided on the broad faces of the structure. In approximately thegeometric center of the coupling space 23 there is placed a small rod 25of a material which is active in the Faradaymagueto optical sense. Suchmaterials include polyirons' and ferrites and are often referred tosimply as ferrites and will be so designated in the presentspecification and claims. These materials, and their polarizationrotation capabilities, are more fully described in the Luhrs and TullPatent No. 2,644,930, issued July 7, 1953.

The rod 25 must be supplied with a magnetic field and this field may beobtained by various arrangements of coils or permanent magnets within orwithout the waveguide but for illustrative purposes is shown as beingobtained from a coil 26 wound directly around the rod 25. The leads 27and 28 support the coil 26 and rod 25 and pass through holes in thewalls 14 and 15. The leads are connected to a source of voltage 29.

In the absence of the rod 25 and coil 26, the wave energy in arm C woulddivide equally between arms E and F, the energy passing to arm E beingshifted in phase an additional 45 or a total of while theenergy passingto arm F would be shifted an additional or a total of The energy in armD would also divide equally between arms E and F, the portion passing toarm B being shifted an additional 135 or a total of 270 while thatappearing in arm F would be shifted an additional 45 or a total of 180.The two components entering arm E would thus cancel since they would beof equal amplitude but opposite phase while the two components enteringarm F would be in phase with each other and therefore additive. In otherwords, all of the power would appearin arm F, none of it appearing inarm E.

Applicant has discovered that the presence of the rod 25 and coil 26without any current flowing in the coil 26 upsets the balance of thejunction so that power appears in both arms E and F. Application of a D.C. voltage of one polarity to the conductors 27 and 23 causes the powerin arm E to increase while the power in arm F decreases. oppositeeffect, that is, the power in arm F increases while the power in arm Edecreases.

The exact nature of the fields existing in the region of the couplingspace 23 with the rod 25 magnetized is not fully understood. It isbelieved, however, that the polarization rotation caused by the ferriterod 25 interacts with the complex modes introduced by the coupling space23 to cause a resulting overall phase shift the magnitude of whichdepends upon the magnitude and polarity of the magnetic field passingthrough the rod 25. What- Reversal of the polarity causes the,

It isthusseenthat applicant has provided apparatus fordivertin'gmicrowave power from on'e'arm toanother regardless of whether the powerlevel is low or-high. The

inductance ofthe small ferrite rod 25 'and the small coilf 26 are smallenough that a rapid switching action may be;-

obtained by exciting the coil with' alternating curl-ent 'What isclaimed is: V 1. A- microwave switch comprising twocollinear wave guideshort slot" hybrid junctions axially aligned, eachof] said junctionsincluding a couplingvspace, a ferrite ele-- ment in the coupling spacein one of said junctions, and means for applying a magnetic fieldto saidelement perpendicularto the narrow waveguide walls.

2. A microwave switch comprising two waveguide short slot hybridjunctions axially aligned, each of said junctions including'a couplingspace, a ferrite element occu pying a portion ofthe coupling space ofone of's'aid junc' tions, and means for applying a magnetic field tosaid element perpendicular to the narrow waveguide walls.

A microwave switch'comprising, two waveguide short 'slot hybridjunctions axially aligned, each of said junctions including a couplingspace, a ferrite element positioned approximately in the center of thecoupling space of one'of; saidjunctions, a coil wound aroundsaid'element, the axis of said coil being perpendicular to the narrowwaveguide walls, and a source of voltage 'connected' tosaid coil;

4. A microwave switch comprising, two collinear wave- 1 tionsincludingacoupling space, an element activein the guide short slot hybridjunctions, each of said junc- Faraday magneto optical sense positionedin approximately the geometric center of the coupling space of one ofsaid junctions, a coil wound around said element and having its axissubstantially parallel to the broad waveguide walls and perpendicular tothe narrow waveguide walls, and a voltage source connected to said coil.

5. A microwave switch comprising, a pair of rectangular. waveguideshaving a common narrow wall, two intermediate portions of said [commonwall being cut away thereby forming two coupling spaces in whichmicrowave energy in said waveguides may interact, an element active inthe Faraday magneto optical sense positioned in approximately thegeometric center of one of said coupling spaces, a coil wound aroundsaid element and having its axis substantially parallel to the broadwaveguide walls and perpendicular to the narrow waveguide Walls, twoconductors connected respectively to opposite ends of' said coil andextending through holes in opposite outer narrow walls of said"waveguides, and a source of voltage connected to said conductors;

References Cited in the file of this patent UNITED STATES PATENTS2,679,631 Korman May 25,, 1954 2,728,050 Van de Lindt Dec. 20, 19552,745,069 Hewitt May, 8, 1956 2,798,205 Hogan .i July 2, 1957 FOREIGNPATENTS 980,648 France. Dec. 27, 1950

